When an image of a bright object is captured by an imaging device that captures an object, unnecessary light around the object can be bright enough and visible, adversely affecting the captured image. Especially when a diffractive lens having a diffraction grating is used, unnecessary light due to unnecessary order diffracted light other than the design order of a diffractive lens is generated, and thus the unnecessary light can be larger compared to the optical system including only an aspheric lens.
There is a conventional technique which reduces the unnecessary light by performing image processing. For example, according to PTL 1, unnecessary light is estimated based on a convolution integral of a point spread function (PSF) of an unnecessary order diffracted light (zeroth order light and second order light) of a diffractive lens and a captured image, and the unnecessary light is reduced by subtracting the estimated unnecessary light from the original image.
Furthermore, according to PTL 2, a plurality of images is captured with different exposure times, unnecessary light is estimated based on an image captured with a short exposure time, and the unnecessary light is reduced by subtracting the estimated unnecessary light from the image captured with a long exposure time.